1. Field of the Invention
The present invention relates to moveable control elements mounted in ducts for the regulation of the rate of flow of gaseous fluid through the ducts. More particularly, the invention relates to control members in the form of louver-blades which are rotated from their ends in shutter-like configurations mounted in ducts to control the rate of flow of gaseous fluid through the ducts.
2. Description of the Prior Art
The utility boiler represents a class of industrial equipment which uses extremely large volumes of gaseous fluids. The term gaseous fluids includes both the combustion air flowed to the burners of utility boilers and the gaseous products of combustion flowing from the boilers. It is not necessary to refer to specific rates of flow to emphasize the large quantity of these gaseous fluids needing control as they flow to and from the multi-story utility boilers. It is sufficient to point out that the gaseous fluid through these ducts will range in pressure up to 60 w.g. at temperatures up to 800.degree. F. The ducts, in cross section, will convey these gaseous fluids with cross sectional areas up to about 700 sq. ft. Prior workers in the art have long attempted to solve the problem of control of gaseous fluids in ducts ranging up to the foregoing size. The thermal and pressure forces of gaseous fluids to and from the utility boilers cycle over ranges which place large stress upon the ducts with which these gaseous fluids are conveyed. Certainly the prior art has directed efforts to controlling the "ballooning" of the duct sides under the pressure and temperature stresses. The dimensions of the ducts may bounce up and down with thermal and pressure variation, but certainly elements placed in the ducts to control the gaseous fluid flowing in the ducts must have close tolerances to have any accuracy in regulating the gaseous fluids flowing through the ducts.
The prior art has developed within the concepts of frames mounted within the ducts and various forms of moveable control elements, such as dampers, to regulate the sizes of resulting openings through the frames to establish the amount of gaseous fluid flowing through the ducts. The prior art has not solved the problem of successfully resisting the stresses placed upon the frames and dampers which change their dimensions. As the demand for greater sizes of ducts has appeared, the crude arrangements of the prior art have fallen short in efficiently providing the dimensional stability required for accurate control of the gaseous fluid passing through the duct.
Not only has the prior art failed to produce a sufficiently sturdy frame, but the louvers mounted in the frame have been cumbersome devices which have been difficult to fabricate to various sizes and maintain dimensional stability relative to the frame. Additionally, the prior art has failed to solve the problem of arranging the frame and damper mating surfaces to eliminate obstructions upon which debris accumulates.